Population replacement using refractory vector strains has been proposed as a means to control the transmission of parasitic diseases. Our ultimate objective is to produce vector strains that are refractory to parasites and viruses and that can be used in novel disease control strategies. The abilities to make and test genetically-altered vector strains in the laboratory are necessary prerequisites to any field trials. Our specific aims are to develop methods for assaying the effects of hybrid gene contructions on the development and replication of parasites and viruses in the vector mosquito, Aedes aegypti. The approach that we are taking includes the use of molecular biological techniques to isolate promoters of genes expressed abundantly in specific tissues of the vector and the linkage of the promoters to marker genes to analyze their function in a transient expression assay. Eventually the marker genes will be replaced by select DNA sequences that will be tested for their effects on parasite transmission. The efficiency of the assay will be improved by isolating mosquito autonomously replicating sequences and incorporating them into the hybrid plasmids. This assay will allow us to test hybrid gene constructs for their effects on parasite transmission in the absence of a system for producing stable transformed mosquitoes. We anticipate that our work will lead to the production of refractory strains that can be used in population replacement strategies.